Sensors using capacitive transducers are commonly used to convert variations in a measured pressure (or other variable) to variations in capacitance. The variations in capacitance are then processed to convert them to variations in voltage, the result being an output voltage that corresponds to the pressure (or other variable) being measured.
The processing circuitry which converts capacitance variations to voltage variations frequently uses one or more oscillators whose tuning can be varied by changes in the capacitive transducers. Another technique which performs the same function in a different way is described in U.S. Pat. No. 4,250,452.
Although the conventional techniques for converting variations in capacitance to variations in voltage perform their function in a reasonably reliable manner, certain improvement are desirable. For example, the conventional techniques use processing circuitry which is fairly complex and which includes a relatively large number of components. Reducing the number of components and circuit complexity would not only reduce cost, but permit easier and more complete compensation for temperature changes.
Another improvement which is desireable and significant is to reduce the sensitivity of the processing circuits to stray capacitance. As is described in more detail later herein, the effects of stray capacitance can mask desired variations in the capacitance of the capacitive tranducers. Also, it is desireable to eliminate the sensitivity of the processing circuitry to amplitude and frequency variations in the oscillator signals and/or switching signals which are conventionally used with this type of processing circuit.